This invention pertains to tractor-trailer brake systems and more particularly to a fluid power circuit providing a selective operation of the trailer brake system.
A trailer brake system is usually coupled with a tractor hydraulic system. Consequently, the actuation of the tractor brake simultaneously causes the braking of the trailer. Such an arrangement causes a problem during the field operations for an agricultural vehicle, such as a tractor or the like, connected with a wagon or other implement as a trailer unit. A trailer brake is added to an auxiliary hydraulic system of a tractor in the line from a pump to a draft control auxiliary valve. This valve is actuated by pressure in one of the main brake lines. Such pressure increases the pressure of the auxiliary pump output flow going to the brakes on a trailing wagon. When two brake pedals of a tractor are locked together for a road transportation, the tractor-trailer unitary system works well. But in the field, use of independent brake pedals on a tractor in order to make a sharper turn actuates the trailer brakes. Thus, the tractor's ability to turn is retarded.
The subject invention permits a selective field operation of a tractor-trailer brake system by hydraulically coupling the trailer brake system with the tractor brake system only when two independent tractor brakes are synchronously engaged.